Water Hoglouse (Asellus aquaticus)

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A Water Hoglouse photographed to show the underside. The dark line is the gut and the head is to the right. Note the gills under the rear segment of the abdomen

IDENTIFICATION: Also known as the Water Slater. The word slater often refers to woodlice and essentially this is an aquatic woodlouse that is typically around 10mm but will grow larger. The body is flattened and segmented (9 including the head) with 6 pairs of legs and two pairs of antennae (characteristic of crustaceans). The first pair is long. The colour is a mottled brown, blending in well with its environment. Females are larger than males and have a brood pouch for carrying eggs (seen in spring as white clusters) and young under the abdomen.Under the telson (tail piece) there is a set of five gill plates and the legs are free of the segments above, projecting well away from the body. There are a number of different species but A.aquaticus and A.meridianus are the most prolific and widespread in northern Europe. In the Mediterranean there are different genera of Isopods found in freshwater. They prefer stagnant water, ponds and slow-moving rivers. Here they scuttle around over the weed and under the debris at the bottom.

ECOLOGY: They are common benthic (bottom) dwellers, living amongst rooting debris of leaves. As a consequence they are most likely in still water or the edge of slow moving streams/rivers. They feed on the decaying matter including dead animals. It is a crawling creature, scuttling around rather than swimming. It ventilates the gills under the last segment of the body, often by protruding them out of the decaying matter with the head buried. It is adapted to survive on low oxygen levels living in this area. As a consequence it is able to tolerate moderately polluted water.

Classification:
Kingdom	Animal
Phylum	Arthropoda
Class	Crustacea
Order	Isopoda